The present invention relates to an insulating film and an electronic device, and more particularly, it relates to an insulating film suitably applied to an electric field effect type transistor and a metal-insulator-metal (MIM) capacitor, and to an electronic device having the insulating film. Furthermore, the present invention relates to electronic devices, such as a MOS field effect transistor which has the semiconductor substrate mainly constituted by Si (silicon) and a gate insulating film using the layered perovskite substance which is epitaxially grown directly on it.
In order to carry out a miniaturization of ULSI (ultra large scale integration) devices and to reduce power consumption, it has been desired to make the gate insulating film thin. Conventionally, in order to keep the amount of electric charges induced to the channel of FET (Field Effect Transistor), the technique of enlarging a capacitance has been taken by making the gate insulating film thin. As the result, making SiO2 film which is the gate oxide thin is promoted, and it is going to reach even the thickness below 10 angstroms (1 nm) now.
However, as long as the SiO2 film is used, a gate leak current becomes large and power consumption is no longer pressed down from loss of standby power requirement. For example, although MOSFET operates normally with SiO2 film of 8 angstroms (0.8 nm) of thickness, gate leak current has reached even 1 kA/cm2 and the problem in the field of power consumption is very big.
It is effective to increase the thickness, in order to reduce power consumption. For this reason, the trial to keep the amount of electric charges by using films thicker than SiO2 film is actively examined by employing materials with high permittivity (high-K dielectric). However, generally as for the materials with high permittivity, the band gap tends to become smaller. Actually, in the gate insulating film using a substance with high permittivity like SrTiO3, since the band offset by the side of a conduction band becomes very small, it is difficult to stop the leak current by making the thickness quite thick. Similar situations may take place in the case where other substances which have high permittivity such as (Ba, Sr, Ca) (Ti, Zr)O3, Pb(Zr, Ti) O3, SrBi2Ta2O9, Ta2O5, CeO2 and TiO2 are used.
That is, band offset for silicon with these substances is very small compared with 0.5 eV (an ideal is 1.0 eV or more) of a target. There are materials where the amount of the band offset to silicon is only about 0.1 eV. The same problem exists in the case of MIM capacitors. For example, in a Pt/SrTiO3/Pt capacitor, since the leak current is very large, it is unutilizable.
On the other hand, a laminated type insulating film using two or more layers which consist of an insulating material is proposed (for example, Japanese Patent Laid-Open Publication No.2000-195856, Japanese Patent Laid-Open Publication No.2001-274393, and Applied Physics Letters 78 p3292 (2001))
However, from a view point of the miniaturization for high integration and the request of low power consumption, these laminated-type insulating films and the Ruddlesden-Popper type (Srn+1TinO3n+1) films were not sufficient to realize both higher permittivity and lower leak. On the other hand, an invention about a perovskite type substance which is formed on silicon substrate with an optimized condition is proposed (Japanese Patent Laid-Open Publication No.2002-100767).
However, in the technology described in the above-mentioned Japanese Patent Laid-Open Publication No.2002-100767, the optimum range of the perovskite type substance is sought for gate insulating films. Moreover, it is not taken into consideration about the barrier for electrons. Furthermore, it is not taken into consideration about the shift of the optimum range at the time of introducing “distortion” into Si substrate. For this reason, the optimization in a true meaning is not carried out. In invention indicated in the Japanese Patent Laid-Open Publication No.2002-100767, the optimum range is not specified appropriately, as will be explained in full detail later.